158 VITAMINS A AND CAROTENES 



normal in appearance though probably hypofunctional. The lining of hair 

 follicles is usually hyperkeratotic, and the follicles are sometimes moder- 

 ately dilated with horny plugs enveloping coiled remnants of the hair, but 

 the plugs rarely project above the surface of the skin. Except for occasional 

 mild perifollicular infiltration, the corium is normal. There is no adequate 

 explanation as to why the follicular reactions are so minimal despite the 

 excessive hyperkeratosis in these instances of advanced avitaminosis A, 

 while the intensity of the two reactions is reversed in the more common type 

 of cutaneous change, referred to as follicular hyperkeratosis, usually as- 

 sociated with less marked ocular symptoms or at times with absence of such 

 symptoms. 



In typical follicular hyperkeratosis the follicle cavity becomes greatly 

 distended by a conical or hemispherical plug consisting of concentric layers 

 of keratinized cells cemented together by sebum, within which coiled rem- 

 nants of the hair may be seen. The papules vary in size but rarely exceed 

 5 mm. in diameter. The dilated follicle may be bridged by a loosely adherent 

 scale, or the plug may project above the surface of the skin. When the plugs 

 are expressed, or when they are shed spontaneously after a week or two of 

 vitamin A therapy, gaping holes are left. These gradually diminish in size 

 and rarely leave scars. 



The epidermis between follicles shows varying degrees of hyperplasia 

 and hyperkeratosis; this is most marked as one approaches the margin of 

 the follicle where increased pigment in cells of the basal layers is also a 

 prominent feature, accounting for the hyperpigmentation often grossly visi- 

 ble at the base of the involved follicles. Despite the abundance of keratinized 

 cells on the epidermis and in follicle plugs, providing a culture medium for 

 many bacteria, skin infections are no more common than in normal indi- 

 viduals. Various observers have commented on the rarity of pustulation, or 

 on the fact that acne eruptions on the face, or intermingled with the follicu- 

 lar lesions in other areas of the body, show a much lesser degree of pustula- 

 tion in individuals exhibiting follicular hyperkeratosis. The dermis is normal 

 except for cellular infiltration or mild inflammatory reactions occasionally 

 seen in the perifollicular area. 



The short ducts of the sebaceous glands, lined by stratified squamous 

 epithelium continuous with that of the follicle cavity, also exhibit hyper- 

 keratinization which may lead to blockage of the ducts. There is extensive 

 atrophy of sebaceous glands related to hyperkeratotic follicles, but no evi- 

 dence of hyperkeratosis of the glandular epithelium. Absence of cystic 

 dilation of the glands suggests that duct blockage is not an important factor. 

 None of the observers have tried to explain this atrophy. It seems possible 

 that the cause may lie in the altered duct epithelium, which is generally 

 regarded as the source of new cells for the epithelium of the glands proper. 



